The goal of this project is the isolation and characterization of the protein product of the recA gene of Escherichia coli. This recA protein is known to be an essential component of the systems for DNA repair and recombination in this organism. A transducing bacteriophage carrying the recA gene has recently been isolated. This phage will be used to effect radiochemical identification of the recA protein by infection of heavily UV irradiated host bacteria followed by addition of labeled protein precursors. The information about the properties of the recA protein gained in this way will be used to guide purification of the protein to homogeneity. The purified recA protein will be examined for binding to DNA, presence of an intrinsic nuclease, ability to inhibit or stimulate nucleases, and ultimately to attempt to reconstitute early steps of recombination in vitro.